<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>盒子尺寸背景色</title>
    <style>
        /* 最外层容器， 浏览器高度 */
        html{
            height: 100%;
        }
         /* 向html要 */
        body{
            height: 100%;
        }
        .box{
            width: 100%;
            height: 50%;
            background-color: aqua;
        }
    </style>
  </head>
  <body>
    <div class="box"></div>
  </body>
</html>
